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Variation and Inheritance Vocabulary
Variation, Inheritance, and Genetics Vocabulary Allele: variant (often mutated) forms of a gene Base Pairing Rules: complementary base pairs formed by hydrogen bonding. The base adenine (A) always pairs with thymidine (T, or U, uracil, in RNA molecules) and the base guanine (G) always pairs with cytosine ©. Centromere: attachment points for spindle fibers during cell division Chromosome: a large DNA molecule carrying an array of genes Diploid: containing two copies of each chromosome Dominant: an allele that expresses its phenotypic effect even when heterozygous with a recessive allele Fertilization: fusion of two gametes to form a zygote Gametes: haploid cells for sexual reproduction (eggs and sperm or ovules and pollen) Gene: a stretch of nucleotide sequence on a chromosome, usually encoding protein (or active RNA) Gene Expression: synthesis of a gene product in a cell by RNA transcription and (usually) protein translation. Genotype: the genetic constituents within an organism Haploid: containing one copy of each chromosome Heterozygous: containing two different forms of a particular gene allele Homozygous: containing the same alleles for a certain trait Independent assortment: Mendel's law, stating that allele pairs separate independently when gametes form Locus: the specific position of a gene (its DNA sequence) on a chromosome Messenger RNA (mRNA): copied nucleic acid gene sequences that will be translated into protein in the cytoplasm. Mutation: permanent changes to a DNA sequence (substitution, deletion, insertion) Ontogeny: development of an organism, from embryo to adult Pedigree: a method using a special chart (or family tree) to determine the pattern of inheritance of a particular trait, especially in the case of human genetic diseases. For pedigrees, males are represented by squares and females as circles, with the filled symbols used to identify individuals that exhibit the trait in question. Phenotype: the visible characteristics of an organism Phylogeny: evolutionary relatedness between organisms. Molecular phylogeny is based on DNA sequence comparisons, rather than simply external characteristics. Probability: the likelihood something will occur Recessive: an allele whose phenotypic effect is not expressed in a heterozygote Replication: the formation of two DNA molecules from one. Each strand of the double helix provides a template for formation of new daughter molecules via base pairing interactions. Ribosome: the cytoplasmic organelle responsible for linking amino acids into proteins Sequence: a linear arrangement of subunits in a molecule (e.g. DNA sequences consists of runs of the nucleotide bases GATC, while protein sequences consist of stretches of amino acids, linked together). Like letters in a word, these molecular sequences must be in the correct order to carry information and function correctly! Spindle: cytoskeleton components responsible for segregating chromosomes during cell division Test cross: a method to determine the genotype of an individual that exhibits a dominant trait by crossing it with a homozygous recessive individual. If any progeny show the recessive trait, the genotype must have been heterozygous. Transcription: the process of copying a DNA gene into RNA (by RNA polymerase) Transfer RNA (tRNA): small RNAs that carry amino acids to the ribosome, to insert them into newly synthesized proteins based on the triplet code, via complementary 'anti-codon' loops Translation: the process of protein synthesis, based on the genetic code and performed by the ribosome. Zygote: the initial cell of a new organism, formed by fusion of two gametes in sexual reproduction.